The invention relates to a process for preparing triethylenetetramine substituted by at least one methyl group (Me-TETA or methyl-substituted TETA compounds). Me-TETA is prepared by hydrogenating biscyanomethylimidazolidine (BCMI) in the presence of a catalyst. The present invention further relates to methyl-substituted TETA compounds as such. The present invention further relates to the use of methyl-substituted TETA compounds as a reactant or intermediate in the production of, for example, coatings or adhesives.
The preparation of (unsubstituted) triethylenetetramine (TETA) is general knowledge. TETA belongs to the group of the ethyleneamines, the best known representatives of which are the short-chain ethylenediamine (EDA) and diethylenetriamine (DETA). Ethyleneamines are suitable as starting materials for the production of numerous end products in different branches of industry, for example in the epoxy sector. For instance, ethyleneamines are suitable for producing coatings, adhesives, adhesion promoters, plastic or polymers. The chemical composition and the properties of the end products thus produced are influenced greatly by the selection of the ethyleneamine as the reactant or intermediate for the production of such end products.
TETA is obtained, among other ways, as a by-product in the preparation of short-chain ethyleneamines such as EDA and DETA. For instance, EP-A 222 934 relates to a process for preparing higher alkylenepolyamines by reacting a vicinal dihaloalkane with an excess of ammonia in the aqueous phase with addition of a strong base to form an imine intermediate, which is then reacted with an alkylenepolyamine to form the higher alkylenepolyamine. A suitable vicinal dihaloalkane is especially ethylenedichloride (EDC or 1,2-dichloroethane). The alkylenepolyamines used are especially ethylenediamine or higher ethyleneamines such as DETA, but also TETA and tetraethylenepentamine (TEPA). These processes (EDC processes) give a mixture of different ethyleneamines (linear ethyleneamines such as EDA, DETA, TETA, TEPA or higher ethyleneamines, and cyclic derivatives such as piperazine (Pip) or aminoethylpiperazine (AEPip)). According to which ethyleneamine is added to the EDC and NH3 reactants, the reaction mixture comprises a corresponding proportion of higher ethyleneamines.
In addition, there are also selective processes for preparing TETA. Such a process is described in WO 2008/104582, according to which TETA is prepared by hydrogenating ethylenediaminediacetonitrile (EDDN) over a catalyst. EDDN in turn is obtainable by reacting EDA with formaldehyde and hydrogen cyanide (HCN). The reaction of EDA with formaldehyde and hydrogen cyanide can be performed in different variants, for example to form the formaldehyde cyanohydrin (FACH) intermediate, by first reacting formaldehyde and hydrogen cyanide in the absence of EDA. According to the selection of the reactant concentrations, as well as EDDN, the corresponding mononitrile compound ethylenediaminemonoacetonitrile (EDMN) can be formed additionally. The preparation of TETA by direct hydrogenation of EDDN is shown in scheme 1 below:

An alternative process for direct hydrogenation of EDDN is described in US-A 2006/0041170, according to which, before the hydrogenation, different protecting groups are attached to the two amino functions of EDDN. After the hydrogenation, the protecting groups are removed again to form (unsubstituted) TETA salts. For instance, two different protecting group methods using benzaldehyde are disclosed, in which no hydrogen but lithium aluminum hydride is used. In a third method, the hydrogenation is performed with hydrogen in the presence of a Boc protecting group. A disadvantage of the process described in US-A 2006/0041170 is especially that it is a multistage hydrogenation process, in which the EDDN reactant used first has to be chemically derivatized (protecting groups) in order to perform the hydrogenation. After the hydrogenation, the protecting groups have to be eliminated again in several reaction steps, which initially give (unsubstituted) TETA as the salt and not in the free base form.